The present invention relates to a method and apparatus for the transmission of communications signals in a wireless network. More particularly, the present invention relates to a method and apparatus for enhancing spectrum utilization at a wireless communications transmission site.
In a wireless communications system, a wireless carrier is often limited in the amount of radio frequency spectrum it can use in the operation of the site. For example, in an e-band license, a wireless carrier may only be allotted 5 MHz of spectrum to use for transmitting wireless signals. This 5 MHz of spectrum must be divided into channels on which wireless signals are transmitted. In a typical configuration, 30 kHz channels are used, which means that a 5 MHz spectrum must be divided into approximately 166 different channels. In this manner, a wireless carrier, at a particular wireless communications site, is limited to these 166 different channels.
Further limitations on the use of these 166 different channels are imposed by the equipment used in a wireless communications site. Depending on the type of equipment used, not all of the 166 channels may be available for transmission at a particular time. The inability to use most of the 166 channels creates difficulty in the operation of the wireless communications system.
If the full 5 MHz of spectrum cannot be utilized, then additional wireless communications sites may need to be constructed. The construction of a wireless communications site involves considerable time and expense. A typical site, such as a cellular site, involves the construction of a tower and an accompanying building to house the electronic equipment necessary to operate the site. Land must be purchased, zoning regulations must be complied with, funds for construction must be outlaid, and time must be invested in constructing the site. Therefore, it is desirable to avoid constructing additional sites by fully utilizing the available spectrum allotted to a wireless carrier.
FIG. 1 illustrates a conventional configuration of a wireless communications site. This site 100, which is typically a cellular site, generally includes a set of radio frequency sources 105, a set of Auto Tune Combiners 110, a band pass filter 115, a multicoupler unit 120, an antenna 125, a radio frequency test loop device 130, and a multicoupler 135. All of these components except the antenna 125, are typically housed in a small building at the wireless communications site. The antenna 125 is typically mounted to a tower which is also at the site.
In the typical configuration of FIG. 1, the set of radio frequency sources 105 are interconnected to the set of Auto Tune Combiners 110. The set of Auto Tune Combiners 110 is then connected to band pass filter 115 which is then connected to multicoupler unit 120. Multicoupler unit 120 is interconnected to antenna 125 and radio frequency test loop device 130. Radio frequency test loop device 130 is connected to multicoupler 135, which is then connected to radio source 105.
Typically, the set of radio frequency sources 105 comprises multiple radios—in this case, six 30 watt radios. Each of these 30 watt radios is typically housed in a cabinet contained within a small building adjacent to the tower at the wireless communications site. Each of these 30 watt radios generates a signal at a particular frequency or on a particular channel that is later transmitted on antenna 125. In this configuration of six radios, the transmission on antenna 125 is limited to six different frequencies or six different channels. Generally, the number of radios is limited only by the spectrum that is assigned to a wireless carrier as well as the space available in the cabinet and small building at the wireless communications site. In other typical configurations, more than six radios are employed at a given site.
The signal generated by each of the 30 radios then passes to one of the Auto Tune Combiners 110. In the typical configuration, each individual radio has associated with it a single Auto Tune Combiner. In this case, the set of Auto Tune Combiners 110 comprises six separate Auto Tune Combiners that are cabled together. Usually, these six different Auto Tune Combiners are all interconnected to an Auto Tune Combiner Controller (not shown), which controls the operation of the six individual Auto Tune Combiners. An Auto Tune Combiner functions to combine all of the different signals produced by the radios to get maximum power out to the antenna. In this case, the six 30 watt radios produce six signals at six different frequencies. The Auto Tune Combiner takes these six signals at the six different frequencies and combines them so as to form one signal that is transmitted by antenna 125.
After the Auto Tune Combiners 110 process the signals from the six radios 105, the resulting output is passed through band pass filter 115. Band pass filter 115, in a typical configuration, operates to ensure that the transmission on antenna 125 is within a prespecified frequency range. In this case, a wireless provider with 5 MHz of spectrum available would configure band pass filter 115 so that any signal transmitted on antenna 125 would be within the 5 MHz spectrum.
After the signal is filtered by band pass filter 115, it passes to multicoupler unit 120. Multicoupler unit 120 serves typically as a connection point for antenna 125 as well as a sampling point for radio frequency test loop device 130. A coaxial cable typically connects multicoupler 120 to antenna 125. It is across this cable that the signal is sent to antenna 125 for transmission. In addition, multicoupler unit 120 has two test points, a forward signal test point and a reflected signal test point. The forward signal test point of multicoupler unit 120 is connected to the forward port of radio frequency test loop device 130 and the reflected signal test point on multicoupler unit 120 is connected to the reflected port of radio frequency test loop device 130.
Radio frequency test loop device 130 (RFTL) samples the forward and reflected signals from multicoupler unit 120. The forward signal path is the path taken by the signal that is transmitted on antenna 125. The reflected path is the signal or power reflected back from antenna 125. RFTL 130 takes measurements of the forward path signal and the reflected path signal to verify that the six radios are each transmitting at a proper power. The RFTL 130 verifies the power of each frequency and sends signals to the radios to increase or decrease power. Additionally, RFTL 130 verifies that the antenna is operating properly. A control signal is sent by RFTL 130 through multicoupler 135 to each of the six radios contained in radio frequency source 105.
In sum, each of the six radios comprising radio frequency source 105 produces six different signals on six different frequencies. These six different signals are sent to six different Auto Tune Combiners that are cabled together to form Auto Tune Combiner 110. The Auto Tune Combiners combine the six different signals so as to allow maximum power transmission on antenna 125. The resulting signal is then filtered through band pass filter 115 and sent to antenna 125 through multicoupler unit 120. RFTL 130 samples the forward and reflected paths of the resulting signal from the forward and reflected connections on multicoupler unit 120. RFTL 130 then performs measurements on the forward and reflected paths to determine whether or not the radios are operating at the proper power as well as whether the antenna itself is operating properly. RFTL 130 then sends a feedback signal through multicoupler 135 to each of the six radios comprising radio frequency source 105.
The typical configuration described with reference to FIG. 1 may be implemented with an Ericsson RBS 884 system. This system typically comes in two different frequency bands, 1900 MHz and 850 MHz. Each of the components of the Ericsson RBS 884 system have certain limitations which constrain the number of channels that can be used in a given frequency spectrum.
The Auto Tune Combiners of this system are specified by Ericsson to require a 21 channel separation. In this case, channels are 30 kHz apart so that a 21 channel separation requires 630 kHz of spectrum. In the example of FIG. 1, this means that each of the six different radios contained in radio frequency source 105 must generate radio signals with frequencies that are at least 630 kHz apart. In a 5 MHz spectrum, this means that at most eight radios may transmit signals on antenna 125 at the same time.
This limitation is illustrated more clearly in FIG. 2A, which is a table depicting the 166 available channels in a 500 MHz spectrum divided into 21 different sets. To honor the 21 channel separation specified by Ericsson, the radio frequency source 105 which comprises multiple radios may only operate on one set of the channel sets depicted in FIG. 2A. As can be seen, the channel sets each contain channels that are separated by 630 kHz or 21 channels. In the typical configuration of FIG. 1, the multiple radios of radio frequency source 105 would be able to use, for example, channel set two which comprises channels 2, 23, 44, 65, 86, 107, 128 and 149. The multiple radios of radio frequency source 105 would not be able to use any of the other channels depicted in the table of FIG. 2A because each of these other channels is closer than 21 channels to the given channel set. Practically, this means that out of a possible 5 MHz spectrum comprising 166 30 kHz channels, only eight different channels can be used at the same time. This greatly limits the amount of capacity at a particular wireless communications site.
Through experimentation, the inventors have found that the Auto Tune Combiners of the Ericsson RBS 884 system, without any additional manipulation, can operate with an 11 channel separation. In this case, the signals generated by the radios of radio frequency source 105 must be 11 channels or 330 kHz apart. This greatly increases the number of frequencies that can be used at the same time by wireless transmission system 100. For example, each of the six different radios of radio frequency source 105 will be able to use six different channels that are 11 channels or 330 kHz apart simultaneously. FIG. 2B depicts channel sets that are 11 channels apart. In FIG. 2B, the entire 166 channels of a 5 MHz spectrum are divided into 11 different sets. Each of these 11 different sets contains channels that are 11 channels or 330 kHz apart. As can be seen, each of these sets contains at least six channels. Therefore, each of the six radios of radio frequency source 105 can operate simultaneously on the six different channels of a given set of FIG. 2B. Even with this 11 channel limitation, however, as can be seen in FIG. 2B, only 15 out of a possible 166 channels can be utilized at the same time. This greatly limits the amount of capacity that can be handled by a given wireless communications site.
A further limitation imposed by the Ericsson RBS 884 is found in RFTL 130. RFTL 130 requires four channel separation. This means that the radio frequency signals that are transmitted on antenna 125 and sampled by RFTL 130 must be four channels for 120 kHz apart. In the typical configuration of FIG. 1, however, the 11 channel separation of the Auto Tune Combiner 110 takes precedence over the four channel separation of RFTL 130. In other words, the 11 channel separation associated with Auto Tune Combiner 110 must be respected, which would also respect the four channel separation of RFTL 130. In sum, the typical configuration of FIG. 1 requires an 11 channel separation which greatly reduces the amount of a given spectrum that can be utilized.
Applicants have recognized the disadvantage of the limitations imposed by the typical configuration of FIG. 1 and have discovered a method and apparatus to overcome these limitations.